1. Field of the Invention
The invention resides in the field of adjustable workpiece mounting stages and more particularly relates to a modification in the mounting table to which the work pieces are attached to compensate for minor deviations in component fabrication and stage assembly.
2. Description of the Prior Art
Precision positioning stages of the type relating to the invention are disclosed in U.S. Pat. Nos. 4,652,095 and 5,077,620 issued to the applicant. In the first of these, the device described employs an adhesive assembly concept for a stage utilizing two end plates having grooves for receiving a pair of parallel smooth cylindrical rails and a mounting table slidably disposed between the plates.
In the second of these, which is an improvement of the first, there is disclosed an electrical motor, gear system, and encoder mounted on an additional plate also disposed between the rails, the motor being operationally connected to the mounting table by a threaded rod such that the table is moved by actuation of the motor.
In the manufacture and construction of these precision devices, great care must be taken in fabricating the component parts and assembling them into a finished unit. Some tolerances must be within one or two ten-thousandths of an inch for both fabrication and assembly in order to achieve a unit which will function properly over a period of time. It has been found that even the most rigorous shop standards will not prevent the limited performance and possible failure of a percentage of units which is greater than desirable. Further, additional units which function well upon delivery will, over a period of time, wear to the point of unacceptable performance. The present invention is intended to alleviate the above mentioned problems in the interaction of the two main components of these stages, i.e. the rails and the mounting table which moves between them. This is accomplished by a modification to the mounting table providing a take-up mechanism to compensate for minor deviations in component fabrication and assembly.
The invention may be summarized as a compensation or take-up mechanism to reduce the requirement for extreme accuracy in the subject stages, to prevent excessive looseness or tightness in the back and forth motion of the mounting table on the rails, to prevent jogging, i.e. abrupt or non-linear motion of the table and generally to provide a cushioned fit between the table and the rails. The above objectives are achieved by disposing a pair of spaced projections, each having a groove at one edge of the table to engage one of the rails and a single projection, having a groove, intermediate the pair of spaced projections at the opposite edge of the table to engage the other of the rails. The grooves are arranged to be substantially parallel to the upper and lower planar surfaces of the table. An elongate slit parallel to the rails and disposed adjacent to the single projection forms a leaf spring arrangement urging the grooves into engagement with the rails, the table being constructed of metal or plastic chosen to provide the desired spring action.
According to the invention there is provided a component precision positioning stage, comprising a pair of straight smooth unthreaded rails secured in spaced apart parallel relationship, a component mounting table slidably mounted to and disposed over said rails, said mounting table being a planar rectangular member having three inwardly facing rail engaging grooved projections disposed adjacent opposing edges of the table, two said grooved projections being spaced apart on one of said opposing edges and engaging one of the rails and the other of the grooved projections being centrally positioned adjacent the other of the opposing edges and engaging the other of the rails, and a slot in said table, closed at its ends, parallel to and in close proximity to the opposing edge of the other of the grooved projections, to define a leaf spring arrangement biasing the grooved projections together whereby grooves of the grooved projections resiliently engage the rails.
Preferably the table has a central threaded bore positioned to engage a threaded rod adapted to be driven by a stage drive means, the three grooved projections form a triangle of rail engaging locations on the table with said two grooved projections disposed at one opposing edge of the table and the slot extends to closely adjacent the opposed ends of the table.
Also according the invention there is provided a precision component positioning stage comprising:
a) first and second smooth straight unthreaded cylindrical rails supported in spaced apart parallel relationship;
b) a component mounting table defining first and second grooves spaced along and engaging said first rail and defining a third groove intermediate of the first and second grooves and engaging said second rail; and
c) a pair of cantilever springs defined by the table to bias said grooves inwardly into engagement with said rails whereby deviations from a true linear path are prevented by said bias.